1. Field of the Invention
The present invention is in the field of electromagnetic beam radiation systems and more particularly in the area of polarization image rotation switching systems.
2. Description of the Prior Art
Several prior art systems have been developed which project orthogonally oriented elongated beams for the purpose of providing guidance information to beam-rider type missles.
U.S. Pat. No. 3,398,918 discloses two embodiments of an optical beam-rider guidance system beam projector. In the first embodiment, four elongated beams of infrared electromagnetic radiation are separately generated and amplitude modulated to produce four distinguishable walls of a guidance control corridor. Each beam is derived from a separate laser generator positioned to emit a beam of light through a pair of crossed polarizers separated by an amplitude modulating birefringent medium. The birefringent medium is controlled by electrically modulating signals applied to opposing electrodes in the medium. The modulated beam is of plain polarized as it is transmitted through the second of the two crossed polarizers. It is then imaged by a pair of anamorphic lenses to have an elongated cross-section. The lenses are servo-controlled for relative movement to vary the size of the cross-sectional length of the elongated beam as the missle is predicted to be located down range after launch. By simultaneously controlling the size of all four separately projected beams, the control corridor is intended to maintained at a constance size with respect to the missle throughout its flight path.
The second embodiment of the guidance system beam projector in U.S. Pat. No. 3,398,918 illustrates the use of two orthogonally oriented cross-sectional beams that are simultaneously transmitted and scanned across an overlapping control area in space. The two beams are generated by a common laser generator. The beam from the generator is split in two beams which pass through corresponding amplitude modulators where they are modulated at different frequencies. The modulated beams are fed to separate scanners and anamorphic optic systems where the beams are imaged in orthogonal relationships and scanned in orthogonal directions.
U.S. Pat. No. 4,111,385 discloses a laser beam-rider guidance system which employs a synchronization beam for defining the guidance control field in space. One embodiment shows the simultaneous transmission of the synchronization beam and orthogonally oriented "x" and "y" beams, having separate pulse repetition frequency rates, repeatedly swept through the synchronization beam in non-overlapping time periods to provide coordinate location information to a missle within the synchronization beam control field. Another embodiment shows the use of an "L" junction laser source having two orthogonally oriented junctions that are separately modulated and simultaneously driven to produce the "x" and "y" beams. A rotating, scanning, prism, in combination with separate relay lenses, provides the sweeping movement to the beams with respect to the synchronization beam.
Commonly assigned U.S. Pat. No. 4,186,899 is directed to a controlled beam projector. In a first embodiment, a rectangular cross-section beam of a first size format, emitted from a correspondingly activated source, is formed in size by a clad glass fiber assembly and is directed to a lateral scanner. The scanner is synchronously timed with respect to a rotating beam chopper optical system that performs alternate rotation and de-rotation operations on the projected beams. In a second embodiment, separate rectangular cross-section beam sources are positioned so as to respectively emit orthogonally oriented beam images.